A solid electrolytic capacitor has a solid electrolytic capacitor element encapsulated by a resin or the like. The solid electrolytic capacitor element in general has an anode body, a dielectric layer, a semiconductor layer, a conductive carbon layer and a conductive metal layer which are laminated in this order. The anode body is composed of a porous body obtained by compacting and sintering a powder of valve metal, for example. The dielectric layer is composed of a dielectric coat obtained by anodizing the surface layer of the porous body, for example. An anode lead is connected to the anode body in an electric conductible state, and the anode lead is exposed to the outside of a package of the solid electrolytic capacitor so as to become an anode terminal. On the other hand, a cathode layer is composed of the conductive carbon layer and the conductive metal layer laminated on the semiconductor layer, and a cathode lead is connected to the cathode layer in an electric conductible state so that the cathode lead is exposed to the outside of the package of the solid electrolytic capacitor so as to become a cathode terminal.
The conductive carbon layer is usually made by applying a conductive carbon paste on the surface of the semiconductor layer. A boundary between the conductive carbon layer and the semiconductor layer can be easily separated due to a mechanical stress or a thermal stress, and a gap might be generated. The generation of the gap might result in increasing of equivalent series resistance (ESR) or increasing of a leakage current. Particularly, if the capacitor is left for a long time under high temperature and high humidity, separation at the boundary between the conductive carbon layer and the semiconductor layer can easily progress.
As mentioned above, if another layer such as the conductive carbon layer is laminated on the semiconductor layer, the laminated another layer might be often separated after being left for a long time under high temperature and high humidity in a element for an electronic component comprising a traditional semiconductor layer.
As a method of forming a conductive polymer layer as a semiconductor layer of an element for an electronic component, a chemical oxidative polymerization method and an electropolymerization method are known. Patent Document 1 describes that in the chemical oxidative polymerization method, the conductive polymer layer might be composed of an agmina of fine particles obtained by abnormally growing in one direction around the fine particles as a core. As an improved method of the chemical oxidative polymerization, Patent Document 1 describes a method in which the element surface is impregnated with a conductive monomer and an oxidizing agent and then, ultrasonic vibration is applied so as to make a conductive polymer layer having a thickness evenly adjusted. Also, Patent Document 2 discloses a method of forming a conductive polymer layer in which a solution containing an oxidizing agent and a solution containing a conductive polymer precursor are stuck to a substrate; and temperature, humidity, wind speed and pressure are adjusted so that a specific relationship is implemented in the amount of a solvent in the stuck solution at start of the chemical oxidative polymerization and the amount of a solvent in the stuck solution upon termination of the polymerization to be subjected to the chemical oxidative polymerization.
On the other hand, as the electropolymerization method, Patent Document 3 discloses a method in which a solution of the conductive polymer precursor is stuck to the substrate and the substrate is dried, and then the substrate soaked in an electrolytic solution is electrified. The Document describes that an ESR value is lowered by this method.